Cyclone furnace

ABSTRACT

Ash and cinder are continuously removed from the grate of a cyclone furnace by an ejector device formed as a double skinned member, where the matter removed from the furnace is rapidly cooled and dispersed by the compressed air operating the ejector.

Apr. 8, 1975 United States Patent [191 Stenlund [56] References Cited UNITED STATES PATENTS CYCLONE FURNACE Inventor:

Strimon 110/28 110/28 12/1964 Montgomery........................ 110/28 1.970.109 8/1934 2,518,800 8/1950 Lester, Sr. 3.161133 [73] Assignee:

[22] Filed:

Primary E.\-amt'ner1(enneth W. Sprague Appl' 438193 Attorney, Agent, or Firm1-1o1man & Stern [57] ABSTRACT Ash and cinder are continuously removed from the Sweden........

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BACKGROUND OF THE INVENTION Cyclone furnaces are often used for the combustion of bark and other wood refuse. Such a furnace includes a cylindrical combustion chamber with its axis vertical and is in its lower part provided with a grate and usually also a mechanical stoking device feeding the fuel to the central part of the grate, where the fuel will form a substantially conical mound.

In its upper part the furnace is provided with a number of tangentially directed openings for combustion air, which impart a forceful rotating movement upon the combustion gases.

The diameter of the grate is selected in such a manner with respect to the desired capacity and to the angle of repose of the fuel in question, that an annular passage, free of fuel is formed around the mound of fuel.

Due to the forceful rotation within the combustion chamber a great many unburned particles will be set into movement along the face of the mound, and will eventually reach the annular passage. Bark has a high content of mineral components, and wood refuse is often mixed with sand which has been brought along during the transportation of the logs to the plant. The unburned particles have a tendency of clogging together at elevated temperature, and it often happens that they in the annular passage sinter together with the mineral components of the fuel and clog the openings in the grate.

In order to prevent such clogging it has been proposed to use an ejector in an outlet passage connected to the annular passage. In such a manner it is possible continuously to remove the particles, which greatly facilitates the cleaning of the furnace.

Experience has, however, shown that the particles, of which many still are glowing, have a tendency of baking together and thus to clog the outlet passage and the ejector, respectively.

Summary of the invention It has been found necessary to cool down the particles as rapidly as possibly, whereby they will be transformed into a gritlike material which is harmless in the above mentioned respect. To that end the mouth of the outlet passage turned towards the furnace according to the present invention is formed as a double skinned member, the outer skin being connected to a compressed air conduit and the inner skin being formed as a conically tapering tube, at the end of which remote from the furnace the air expelled from the double skin causes a sub-pressure.

Brief description of the drawing FIG. 1 is a portion of a vertical section through the wall of a cyclone furnace for the combustion of bark, at the outlet passage, and

FIG. 2 is a portion of a horizontal section, as viewed from above, of the portion shown in FIG. 1.

Description of a preferred embodiment The cyclone furnace, which is not fully illustrated, is of well known type and includes a cylindrical combustion chamber, the rotational axis of which is vertical, and which is connected to the furnace of a steam boiler. In the lower portion of the furnace a fixed grate 10 is provided onto the central part of which the fuel is fed by any suitable known mechanical device, for instance a screw stoker.

The diameter of the grate is selected in such a manner with respect to the desired combustion capacity and to the angle of repose of the fuel in question that an annular passage 11, free of fuel will be formed around the burning mound 12 of fuel.

In the upper part of the furnace a number of nozzles for the injection of secondary combustion air are arranged. These nozzles are directed tangentially with respect to an imaginary cylindrical surface, concentric with the axis of rotation, and will bring about a forceful rotation of the combustion gases within the furnace chamber.

In use, a great many particles will collect in the annular passage 11. These particles include ashes and unburned matter sliding down along the face of the mound as well as small, unburned particles carried away from the mound by rotating gases and transported by the latter to the wall of the combustion chamber, where they finally will sink down.

The solid matter within the annular passage 11 is maintained in rotation by the gases and would normally be removed through the openings of the grate, or through an outlet passage provided with an ejector.

The present invention refers to furnaces with the last mentioned type of ash removal, i.e., where the annular passage 11 forms a portion of the grate substantially devoid of openings, and where an outlet passage 14 is formed in the wall 13 of the furnace, just above the level of the grate.

The material rotating in the annular passage, includes ash particles, and mineral components and sand from the bark, as well as still unburned particles of fuel. If these hot, partly still glowing particles are permitted to interrupt their movement, due for instance to the rotation being locally braked, they will sinter together to a glass-like coating.

According to the invention a possibility of rapidly cooling and breaking the particles, immediately upon their exit from the combustion chamber is provided. The mouth of the outlet passage 14 is formed as a double skinned member 15 forming a chamber 16 connected to a compressed air conduit 17.

Into this chamber a conically tapering tube 18 extends and forms the outlet proper. At the free end, 19, thereof, remote from the furnace, a sub-pressure is formed by the air being expelled from chamber 16.

The double skinned member will thus form an ejector, which is known by itself, The important features are that the air in the first hand will cool the walls of the air chamber and thus also the particles passing along the same. A further cooling, as well as a dispersing of the particles will occur when the latter meet the stream of air at the mouth 19 of tube 18.

The outlet passage 14, which is provided with a rinsing opening closed by a stopped 20 in the axial elongation of tube 18, may be connected to the furnace of a steam boiler downstream of the cyclone furnace, or to a solid matter separator of known type.

formed as a unit fitted at the mouth of the outlet passage, turned towards the furnace, said unit including aninner and outer wall enclosing between themselves a chamber, each of said walls being formed in the shape of a conically tapering tube directed away from the furnace, the inner wall defining part of the outlet passage and terminating at a mouth within the outer wall, and a compressed air conduit connected to said chamber adjacent to its furnace end. 

1. In a cyclone furnace having a centrally located grate, means for feeding solid fuel onto said grate to form, in use, a mound of burning matter covering a main portion of the grate, but leaving an annular passage free of fuel around said mould and an outlet passage, opening towards said annular passage and including an ejector device for continuously removing particles of ash and cinder rotating in said annular passage, the improvement which comprises the ejector being formed as a unit fitted at the mouth of the outlet passage, turned towards the furnace, said unit including an inner and outer wall enclosing between themselves a chamber, each of said walls being formed in the shape of a conically tapering tube directed away from the furnace, the inner wall defining part of the outlet passage and terminating at a mouth within the outer wall, and a compressed air conduit connected to said chamber adjacent to its furnace end. 